The present invention relates generally to a vehicle occupant safety system and more particularly to a crash severity determination system having an algorithm which provides a continuously variable or “analog” output for use with continuously variable vehicle occupant safety devices.
Generally, vehicle occupant safety systems include a crash severity determination system having a crash sensor, such as an inertial sensor. The crash determination system determines the severity of the crash and crash type based upon signals from the crash sensor. The crash severity determination system then determines a “stage” of activation for the vehicle occupancy safety devices. Generally, air bags with two stages of potential activation are known. Thus, the crash severity determination system must quickly decide whether to: a) not activate the air bag; b) activate the air bag stage 1; or c) activate the air bag stage 2. Since there is a large difference between each of the three stages (not firing, stage 1, stage 2), it is critical that the crash severity determination system quickly determines the proper severity of the crash and the proper activation stage. A slight error in the determination of crash severity in a discrete output crash severity determination system may result in a determination that the next higher or next lower stage has been reached. The result will be a significantly higher or significantly lower activation force from the vehicle occupant safety devices. For example, there is a significant difference between an airbag not firing and an airbag firing stage 1, and there is a significant difference between an airbag firing stage 1 and an airbag firing stage 2.
More recently, vehicle occupant safety devices, such as air bags and other active restraints, have been developed with continuously variable or “analog” activation levels. For example, some air bag inflators can provide a continuously variable inflation force, rather than just one or two stages. Some seat belt retractors can provide a continuously variable retraction force. What is needed therefore, is a crash severity determination system which takes advantage of the new continuously variable vehicle occupant safety devices.